1. Field
Example embodiments may provide a submount and a laser diode module including the submount, for example, to a submount in which a multi-beam laser diode having a plurality of independently driven light emitting units may be flip-chip bonded to the submount and a multi-beam laser diode module including the submount.
2. Description of the Related Art
In general, high-speed printing in a laser printer and data reproduction/recordation in an optical storage device require a multi-beam laser diode having a plurality of independently driven light emitting units.
FIG. 1 is a diagram of a related art multi-beam laser diode 1. As shown in FIG. 1, the multi-beam laser diode 1 may include a plurality of ridges to form a plurality of light emitting units and electrodes A1, A2, A3, and A4 on an upper surface of the ridges. Electrodes A1, A2, A3, and A4 may be covered with a protective layer 9, which may include openings 9W1, 9W2, 9W3, and 9W4 that expose electrodes A1, A2, A3, and A4, respectively. The electrodes A1, A2, A3, and A4 may be electrically connected with bonding pads PD1, PD2, PD3, and PD4, respectively, by conductive layers L1, L2, L3, and L4. In such a structure, current may be supplied to each of electrodes A1, A2, A3, and A4 from bonding pads PD1, PD2, PD3, and PD4, allowing a plurality of light emitting units to be independently driven.
In the multi-beam laser diode 1, heat generated from each ridge may be emitted through a substrate 2 on a lower part of each ridge, and thermal cross-talk may occur between adjacent ridges.
In the multi-beam laser diode 1, efficiency of the multi-beam laser diode 1 may decrease in proportion to the number of ridges. Assuming that the efficiency of the multi-beam laser diode 1 having one ridge is P, efficiency of the multi-beam laser diode 1 having n ridges may be decreased to Pn. For example, if the efficiency of a multi-beam laser diode with one ridge is 0.5, or 50%, the efficiency of a multi-beam laser diode with 4 ridges may be decreased to 0.54, or 6.25%. In order to prevent reduction of a multi-beam laser diode's efficiency, chip size of a multi-beam laser diode may be reduced and the number of laser diode chips per wafer may be increased. It may be difficult to reduce chip size of the multi-beam laser diode 1 due to bonding pads PD1, PD2, PD3, and PD4.
FIG. 2 shows a related art multi-beam laser diode module, which may overcome the reduced efficiency problem. As shown in FIG. 2, the multi-beam laser diode module may include a laser diode 11 having a plurality of ridges and a submount 44 on which the laser diode 11 may be flip-chip bonded. The laser diode 11 may include electrodes 14 and 21 on a lower surface of ridges of the laser diode 11, and the submount 44 may include bonding pads 45, which may be electrically connected with the electrodes 14 and 21 on an upper surface of the submount 44. Solder layers 46 may be formed on the bonding pads 45 for flip-chip bonding to the electrodes 14 and 21 of the laser diode 11. In the laser diode module shown in FIG. 2, the laser diode 11 may be flip-chip bonded to the submount 44, and heat generated from each of the ridges may be directly transmitted to a heat sink (not illustrated) via the submount 44. Thus, thermal cross-talk may not occur between adjacent ridges. In addition, the large-sized bonding pads 45 may be formed on the submount 44, and chip size of the laser diode 11 may be reduced, thereby increasing efficiency of the laser diode 11. In such a laser diode module, if the laser diode 11 is bonded to the submount 44, the solder layers 46 formed on the submount 44 may protrude at the rear of the laser diode 11 as illustrated in FIG. 3 and a solder “bump” 46′ may be formed. The solder bump 46′ may obstruct laser light from reaching its outlet through the rear of the laser diode 11, and thus sensitivity of the photo diode 50, which monitors laser light, may be reduced.